Electrostatic Printer and two plate capacitors deflecting charged ink droplets

1. Nov 8, 2012

Dester

1. The problem statement, all variables and given/known data

One type of ink-jet printer, called an electrostatic ink-jet printer, forms letters by using deflecting electrodes to steer charged ink drops up and down vertically as the ink jet sweeps horizontally across the page. The ink jet forms 30-μm-diameter drops of ink, charged them by spraying 800,000 electrons on the surface, and shoots them toward the page at a speed of 20 m/s. Along the way, the drops pass through two parallel electrodes that are 6.0 mm long, 4.0 mm wide, and spaced 1.0 mm apart. The distance from the center of the plates to the paper is 2.0 cm. To form the letters which have a maximum hieght of 6.0 mm, the drops need to be deflected up or down at maximum if 3.0 mm. Ink, which consists of dye particles suspended in alcohol, has a density of 800 kg.m^3

What amount of charge is needed on each electrode to produce this electric field

2. Relevant equations

3. The attempt at a solution

I know qE/m, I found m and q and also E via part A I solved, but now I'm stumped, can anyone give me hand?

Last edited by a moderator: Nov 9, 2012
2. Nov 9, 2012

haruspex

How long will a drop take to reach the paper? What vertical velocity will it need to achieve the desired deflection? How long does it have to acquire that velocity? What acceleration does that imply?

3. Nov 9, 2012

Basic_Physics

Doesn't it follow a parabolic trajectory between the plates, sort of acting like a stronger gravitational field?

4. Nov 9, 2012

haruspex

Sure, but most of the deflection (in terms of distance, as opposed to angle) will occur across the 2cm gap to the paper.